Port Townsend, Washington Coastal Digital Elevation Model

Perspective view of DEM

NOAA's National Geophysical Data Center (NGDC) is building high-resolution digital
elevation models (DEMs) for select U.S. coastal regions. These integrated bathymetric-topographic
DEMs are used to support tsunami forecasting and modeling efforts at the NOAA Center
for Tsunami Research, Pacific Marine Environmental Laboratory (PMEL). The DEMs are
part of the tsunami forecast system SIFT (Short-term Inundation Forecasting for Tsunamis)
currently being developed by PMEL for the NOAA Tsunami Warning Centers, and are used
in the MOST (Method of Splitting Tsunami) model developed by PMEL to simulate tsunami
generation, propagation, and inundation. Bathymetric, topographic, and shoreline data
used in DEM compilation are obtained from various sources, including NGDC, the U.S.
National Ocean Service (NOS), the U.S. Geological Survey (USGS), the Canadian Hydrographic
Service (CHS), the Puget Sound Lidar Consortium (PSLC), the Joint Airborne Lidar Bathymetry
Technical Center of Expertise (JALBTCX), Canadian Digital Elevation Data (CDED) and
other international, federal, state, and local government agencies, academic institutions,
and private companies. DEMs are referenced to the vertical tidal datums of Mean High
Water (MHW) and North American Vertical Datum of 1988 (NAVD 88) and horizontal datum
of World Geodetic System 1984 (WGS 84). Grid spacings for the DEMs range from 1/3
arc-second (~10 meters) to 3 arc-seconds (~30 meters).

Developed for the Pacific Marine Environmental Laboratory (PMEL), NOAA Center for
Tsunami Research program in support of NOAA's tsunami forecasting and warning efforts.

Use Limitations

Not to be used for navigation. Although these data are of high quality and useful
for planning and modeling purposes, they are not suitable for navigation. For navigation,
please refer to the NOS nautical chart series.

Produced by the NOAA National Geophysical Data Center. Not subject to copyright protection
within the United States.

While every effort has been made to ensure that these data are accurate and reliable
within the limits of the current state of the art, NOAA cannot assume liability for
any damages caused by any errors or omissions in the data, nor as a result of the
failure of the data to function on a particular system. NOAA makes no warranty, expressed
or implied, nor does the fact of distribution constitute such a warranty.

Composite Shoreline of the Continental United States Derived from NOAA-NOS Coastal
Survey Maps

Washington State Marine Shorelines

Bench Mark Data Sheets with Tidal Datum References

VDatum software v. 2.2.7

VDatum software v. 2.2.7

Lineage Statement

Lineage statement not available.

Processing Steps

All datasets obtained by NGDC were converted to common horizontal and vertical datums
of NAD 83/WGS 84 geographic and NAVD 88, respectively, using FME or ArcGIS. They were
also converted to common file format, ESRI point shapefiles or digital rasters, for
visualization and inspection.

Datasets were visually inspected with ArcGIS and QT Modeler for identification and
editing of data anomalies. Datasets were then compared with overlapping datasets to
ensure data consistency.

xyz files of the bathymetric data were surfaced using GMT's 'surface' tool onto a
1/3 arc-second grid that interpolated to fill empty cells. Points extracted every
10 meters along the coastline were also included to ensure that the bathymetric grid
reached zero at the coast. The resulting Arc ASCII grid was imported into ArcGIS and
clipped to the coastline to remove values over land.

xyz files for each input dataset were gridded using MB-System's 'mbgrid' tool, which
utilizes a high-tension spline interpolation method to fill grid cells with no input
elevation values. Preferential weighting was given to more recent, higher-accuracy
datasets. Gridding was performed in quadrants, each with a 5% data buffer. The grids
were imported in ArcGIS and seamlessly merged to create the final DEM.

The DEM was quantitatively evaluated by converting to UTM-zone coordinates (units
of meters horizontally and vertically) and then creating a slope grid to identify
gridding artifacts in the DEM. A conversion grid was created using VDatum points to
convert the NAVD 88 Port Townsend DEM to MHW.